A number of non-transforming mutants of polyoma virus have been isolated and partially characterized with respect to their interactions with cells in culture. The purpose of the proposed research is to define relationships among temperature sensitive and host range non-transforming viruses, and identify the biochemical function of the genes altered in these viral mutants. Particular objectives are: 1) to determine the number of viral gene functions involved in cell transformation through complementation studies in productive and non-productive infections by non-transforming mutants, 2) to map the sites of genetic alteration in mutant viral DNAs by marker rescue experiments, 3) to define and compare alterations in the histone components associated with viral DNA in mature wild type and mutant virus particles, 4) to determine viruses, with particular emphasis on patterns of histone acetylation.